Production of complete fertilizers



June 8, 1954 G.V A. COLEMAN PRODUCTIN OF' COMPLETE FERTILIZERS Filed Dec. 24, 1952 .LOClOHd d E Z Villa 3:1

lNvENToR L'OZemarz ATTORNEY Patented June 8, 1954 UNITED STATES PATENT OFFICE PRODUCTION F COMPLETE FERTILIZERS Gordon A. Coleman, Petersburg, Va., assigner to Allied Chemical & Dye Corporation, New York, N. Y., a corporation of New York Application December 24, 1952, Serial No. 327,887

(Cl. l1-37) 11 Claims. 1

'This invention relates to the preparation of complete fertilizers, i. e., fertilizers containing nitrogen, phosphorus and potash in available form as plant nutrients.

It has been proposed to acidulate phosphate rock with sulfuric acid, nitric acid, or mixtures of sulfuric and nitric acid with or Without phosphoric acid, ammoniate the acidulated material, add a potassium salt to the ammoniated mixture, granulate, and then dry to produce the fertilizer product. Processes of this type heretofore suggested have a number of disadvantages among which may be mentioned:

1. They usually produce excessively hygroscopic products. This is particularly the case when ernploying nitric acid to acidulate the rock.

2. They require excessively long ammoniation and acidulation treatments, thus reducing the capacity of the equipment.

3. They result in unstable products in that salt constituents, such, for example, as ammonium nitrate, tend to continue to react during storage.

4. They do not result in non-segregating, homogeneous particles in which each particle contains all of the constituents of the complete fertilizer and these constituents are present in substantially the same proportions in all of the particles.

5. They present diiiicult problems of material handling in carrying out the different steps of the process. Thus, such processes involving the use of concentrated acid to eiect the acidulation result in heavy pasty masses which are difficult` to agitate within the acidulator and to move from the acidulation zone to the ammoniators. Furthermore, the physical characteristics of the ammoniated mass are such that it is extremely difficult to move it through the -driers and effect satisfactory drying. Breakdown of the drying equipment due, for example, to the formation of hard masses on the Walls of the kiln driers usually employed, or breakage of the flights or baffles, which eifect movement of the material through the driers, is not unusual.

It is among the objects of this invention to provide a process for producing complete fertilizers of lessened hygroscopicity, which processl results in the production of hard, non-caking granules completely stabilized chemically and substantially each particle of which is a com plete fertilizer, the particles being non-segregating, homogeneous and substantially alike in chemical composition. By completely stabilized chemically is meant that thephosphate isso ,chemically ICombined that'it has little' or no tendency to revert to a citrate insoluble form, also that other salts present have little or no tendency to react further during storage of the fertilizer.

Another object of this invention is to provide a process of producing a complete fertilizer of exceptionally high total plant food content Without reducing the content of secondary plant food such as the calcium and sulfur.

Still another object of this invention is to provide a process or" producing a complete fertilizer employing relatively low cost raw materials, such as phosphate rock, ammonia and nitric acid, in which process the acidulation of the phosphate rock and the ammoniation of the acidulated material is eiiected more eiciently and rapidly than in prior known processes and the condition of the reaction masses in the acidulator, ammoniator and drier is such that they can readily be moved and handled mechanically without fouling the equipment.

Other objects and advantages of this invention will be apparent from the following detailed description thereof:

In accordance with this invention phosphate rock is acidulated with a mixed acid consisting of nitric and sulfuric acids, nitric and phosphoric acids, or nitric, sulfuric and phosphoric acids employing from about '7 to about 20, preferable from about 9 to about 16, equivalents of mixed acid per mol of P205 in the phosphate rock. By an equivalent of acid is meant the quantity of acid which contains one formula weight of hydrogen ion, i. e., a half mol of H2SO4, one mol of HNOa and a half mol of HLePOl. HzPOu for purposes of the present invention is considered a dibasic acid, because during the ammoniation of the acidulated rock dicalcium phosphate is formed, i. e., one hydrogen ion remains with the phosphoric acid. Of the mixed acid from about 40% to about 80%, preferably from about to about 80 of the equivalents of acid is nitric acid. When using a mixture of nitric and phosphoric acids it is preferred to use a mixed acid containing an amount of nitric acid in the upper portion of the range hereinabove given, i. e., '70% to 80% of the acid equivalents are nitric acid. The acidulation reaction is carried out in the presence of from about 15% to about 40%, preferably from about 30% to about 40%, Water based on the total weight of constituents present in the acidulator.

rThe acidulated mixture is Yammoniated employing froml about 0.6 to about 0.8 mols of am-r monia per equivalent of acid used in the acidulation. The ammoniated material as it leaves the ammoniator should have a water content of from about 15% to about 30%, preferably from about 15% to about 18% based on the weight of the material leaving the ammoniator and including the Weight of the potassium salt which is preferably added prior to completion of the ammoniation. During the course of the ammoniation about half of the water introduced into the ammoniator is evaporated. The water content oi the acidulated mixture Withdrawn from the acidulator and introduced intdtheammoniator is therefore adjusted, if necessary, by the addition of water to the acidulated material entering` the ammoniator so that the material leaving-the ammoniator has a Water content within the range` above noted.

As above indicated, potassium in the form of its salts, such as potassium chloride or potassium sulfate, is incorporated in the ammoniated material. porated prior to completion of the ammoniation of the acidulated mixture although, if desired, it may be added after the ammoniation has been completed. Other salt enriching constituents which may be absent from certain soils, such, for example, as the salts ofcopper, zinc, iron, manganese, molybdenum, cobalt, magnesium, boron, may also be incorporated during the latter stages of the ammoniation or after the ammoniation has been completed. Such salts are added in minor amounts, desirably inY the form of the sulfate, chloride or carbonate. The resultant mass is ythen blended -With dry product, recycledY from a subsequentstep of the process, which sub sequent step is hereinafter described, to yproduce a mixture .containing from about 15% to about 45%, preferably from about 25% to about 35% liquid (Water plus dissolved salts) at the temperature-of the blend. The vtemperature of the ain-,- moniated mass leaving the ammoniator desirably is in the range of from about '75 to abou-t100? C., preferably from about 82 to about 93 C. This mixture is then passed through aidrier to reduce its moisture content to 1% or 2%.orless and thereafter cooled.

The phosphate rock -employed in this process may beariy form of phosphaterock commercially available. The rock-may be employed inthe coarse condition it comes fromthe mines, e. g., having a yparticle sise such-that-it passes through a 30 to 40 mesh screen. Surprisingly-:ithas been found that employing mixed acid in--theamount and concentration,hereinabove disclosed, such coarse phosphate rock can be acidulated Vrapidly and efliciently. However, for optimum acidulation at maximum rates, the rock is crushed to a size such that it .passes a.l mesh screen or nner. The rock subjected 4to acidulation may be mixed With, triple superphosphate (Ca(I-I2PO4)2 sub-y stantially free of calcium sulfate) if it is Adesired to produce a fertilizer having a higher P205 oontent than thai-,obtained utilizing only the phosphate present 4in the rock. In general the. amount of triple superphosphate added Y may be up to 30% or even higher, preferably from about 15% to about 20%, based onthe weight of the phosphate. rock. The introduction of triple superphosphate. into the acidulator has the desirable advantage of converting insoluble calcium -phosphatewpresent in the triple super-phosphate to the citrate-soluble form,

Using an amount of mixed acid including nitric acid andsulfuric or phosphoric acid, or nitric acid andmixturesof the latter two acids in the Preferably theI potassium-v salt is .incoramounts above indicated results in substantially all of the calcium in the rock being transformed into dicalcium phosphate and calcium sulfate after the ammoniation treatment. As above noted, the acidulation is carried out in the presence of from about 15% to about 40%, preferably from about 30% to about 40% water. The use of such amountsv o fWater is important not only because it results in a fluid mass which can readily be agitated with consequently more rapid acidulation but also because it permits of the use oavailableless costly .dilute acids. Thus, dilute acids may be used to supply the desired water; wheremoreconcentrated acids are available and are used-so that the Water content oi the reaction mixture does not. fall Within the range indicated.,,enoughy ivaterisadded to the reaction mixtureto provide the desired water content. The acidulation is an exothermic reaction and may be carried out at any desired temperature below that at which substantial loss of nitrogenl compounds., takes place;- The acidulation may be carriedout Without external cooling; byintroducing the rock and the acid at atmospheric' temperatures, the-temperature ofthe acidulated mass .in generalwillnot go above about 749 C.,

at which temperaturelittle or no `loss lof nitrogen compounds takesplace.- By observing the above noted conditions, theacidulation may be eifected in from 5 Vto l0 minutes.

Theammoniation isfcarried out in single or multiplestages.Y As .above indicated from 0.6 to 0.8 mols of ammonia are-used-per equivalent of acid `employed inthe acidulation.` Thisamount of ammonia. will neutralize-al1 free acidand convert phosphoric acid. and calcium nitrate to ammonium phosphate, dicalcium phosphate, and ammonium nitrate.l Theammoniation -is carried out at a temperature close-to theboilingpoint of the4 mixture, preferably: thev armnoniationA is carried out near the-boiling point of the mixture. and toward theend of the' ammoniation the temperatureispermittedtofall to about C.

By. observing theabove noted ,ammoniationconditions the ammoniation mayv befreifected in froml 30..,to lzllvminutes.Y

Ammoniation of the acidulated mass under the Y conditions of temperature, water content and amountof. ammonia-abovel given-.results inY (ai tion mixture which canI readily be handled mechanically.

Employing agmultiple stage ammoniation proced-ure, potassium salts,v such as potassium chlorideandother soil enriching constituents, such :i as those.hereinabove enumerated, are added in the-last stageeof the=ammoniation. Similarly when carryingaouttheiammoniation in a single stage, potassium vchloride and other soil enriching constituents may be. added toward the end of thenainmoniation treatment. By so doing, the

reaction between the potassium salts and the ammonium nitrate to formstab1e salt pairs` is promoted and less -unreacted ammonium nitrate is present-inthef`1nal product with consequentv calgeis,moreeasilybroken up. If-potassium sulfate or ammonium sulfate is added, it is desirable to do so at the beginning of the ammoniation.

The amount of potassium salts added may be varied, but it is preferred to add enough potassium salts to produce a iinal product containing from 7% to 20% of KzO. Other soil enriching agents, if used, are generally added in small amounts to produce a final product containing the desired amount of such other soil enriching agents. rllhus, boron salts may be added in amount to produce a product containing from .02% to .05% boron, preferably 04%; man,- ganese salts are added in amount to produce a product containing .02% to .05% preferably .04% manganese; copper salts are added in amount to produce a product containing .002% to 005%, preferably .004% copper; zinc salts are added in amount to produce a product containing .002% to 005%, preferably .004% zinc; molybdenum salts are added in amount to produce a product containing .001% to 002%, preferably .0015% molybdenum and magnesium salts are added in amount to produce a product containing up to 3% magnesium.

The ammoniated mass enters the blender at a temperature of from about 75 C. to about 100 C., preferably from about 82 C. to about 93 C. Recycled material enters the blender at a temperature of from about 55 C. to about 65 C., preferably about 65 C. The resultant mixture enters the drier at a temperature of from about 60 C. to about 80 C., preferably about 70 C. It exits from the drier at a temperature of from about 100 C. to about 120 C., preferably about 105 C. to about 110 C. The driers may be externally heated, the gas temperatures at the hot end of the drier may be from about 400 C. to about 450 C., preferably about 450 C.; at the cool end of the drier the temperatures of the heating gas may be from about 110 C. to about 150 C., preferably about 130 C. Heat exchange media contacting Wet material should be at a temperature not exceeding about 480 C. and those contacting dry material at a temperature not exceeding about 145 C. to minimize decomposition. 'Ihe product leaving the drier contains not more than about 2% moisture.

Desirably from 25% to 65% of the dried product leaving the cooler is recirculated, mixed with the ammoniated material, and the mixture passed through the drier. An important factor in effecting efficient drying without fouling the equipment is to control the liquid (Water plus water-soluble solids) content of the material entering the drier so that it is Within the range of from about 15% toy about 45%, preferably from about 25% to about 35%. This is accomplished by mixing with the ammoniated material an amount of dry product in nely divided form which will result in a mixture containing a liquid content Within this range. The particle size of the product thus mixed with the ammoniated material desirably is such that 1/3 of the material will pass through an 8 mesh screen and be retained onv a 50 mesh screen and 2/3 will pass through a 50 mesh screen.

The liquid content of the material entering the drier is determined by ascertaining the weight of Water present in the material and adding thereto the weight of the salts present in this material and soluble in Water at the temperature of the material entering the drier. The amount of Water can be determined in any known manner, for example, by drying a sample, e. g., by evaporating it to dryness, and determining the .loss inl Weight 6 0f the dried sample. The amount of salts soluble in Water at the temperature of the material entering the drier can be determined by removing a small amount of the liquid phase from a sample of the material, for example, by applying pressure to the sample and then determining the dissolved solids content of the liquid thus removed by evaporating it to dryness. The per cent liquid phase present may readily be calculated from these data.

From the drier the product passes through a cooler Where it is subjected to a stream of air or other inert gas and is thus cooled to about C.

The dried product employing a mixture of HNOS and H2SO4 or HNOs, II2SO4 and H2PO4 as acidulating agent may contain principally dicalcium phosphate, ammonium phosphate, ammonium nitrate, calcium sulfate, and potassium salts. Employing HNO: and phosphoric acid as the acidulating mixed acid the final product differs from that noted above chiefly in that it contains little or no calcium sulfate. In general, when using phosphoric acid as a constituent of the acidulating agent it is not necessary to use triple superphosphate along with the phosphate rock. In other Words, the increased P205 content of the final product over and above that derived from phosphate rock may come from either the triple superphosphate or the use of phosphoric acid as a constituent of the mixed acid.

In general the iinal product using NI-IOs and H2SO4 as the acidulating medium contains from 9% to 11% by Weight of available P205, from 9% to 18% nitrogen and from 7% to 20% KQO. Employing triple superphosphate or phosphoric acid as a constituent of the mixed acid the iinal product contains from 11% to 15% of available P205, from 9% to 18% nitrogen and from 7% to 20% KzO.

The process of this invention may be carried out batchwise or continuously. Due to the relatively rapid rate at which the acidulation and ammoniation may be carried out and also due to the physical conditions of the materials in each step of the process, i. e., they are in every case in a relatively free-owing condition so that they can be moved mechanically without fouling the equipment, the process of this invention lends itself admirably to continuous production ofthe desired nal complete fertilizer.

The accompanying drawing 4shows diagrammatically a preferred layout of equipment for practicing the process of this invention. It will be understood the process may be carried out in other equipment.

In the drawing i0, Il and l2 indicate storage tanks for the phosphoric, sulfuric and nitric acids, respectively. These tanks communicate through suitable lines with an acidulator, such as a pug mill E3. The nitric acid tank aiso communicates with a fume scrubber lil. In this scrubber iiuorine and nitrogen compounds evolved in the pug mill and passing with the gases removed from the pug mill through the fume scrubbers are scrubbed with nitric acid. The scrubbing medium containing these fiuorine and nitrogen compounds may be treated to recover the silicon iiuoride or may be introduced into the pug mill I3 Without such treatment to recoverv the silicon fiuoride particularly when the quantity of silicon fluoride is small. The gas leaving the fume scrubber is substantially free of uorine and nitrogen compounds.

A storage bin l5 for phosphate yrock and a bin' I1 for storing triple superphosphate communicate desirably through suitable measuring hoppers I8 with the pug mill i3. In lieu of the measuring hoppers I8 the storage bins may be provided with screw conveyors or other feeding devices for feeding continuously to the pug mill the phosphate rock with or without triple superphosphate regulated rates. The mixed acid consisting nitric, sulfuric and/or phosphoric acids may introduced into the pug mill I3 continuously a regulated rate, so that the acidulation takes plane continuously within this pug mill, the acidulated material being discharged continuously through line 19 communicating with an arnmoniator.

As shown in the drawing, this ammoniator consists of threesimilar vessels 20. While the drawing shows three such vessels, it will be understood any desired number may be employed, preferably three or four.

Each vessel Y20 communicates with an ammonia L storage Vtank 2l. The lines leading from this storage tank to each vessel each passes into a vaporizer 22 for vaporizing the liquid ammonia removed from the storage tank 2 l. rlhe gaseous ammonia flows from each vaporizer into the vessel communicating therewith. Each vessel desirably is provided with a motor-driven agitator 23. A water line 24 leads into the first vessel of the series to supply water, if necessary, to provide the desired water content in the acidulated mixture subjected to ammoniation. The vessels 20 are interconnected by-lines 25 for now from one vessel to the next, and the last vessel of the series is provided with a discharge line 26 leading into a blender 2l. A potash storage tank 2S communicateswith the last Vessel of the series through a suitable measuring hopper 20. In lieu of this measuring hopper-potash storage tank 23 may be provided with a screw conveyor or other device for feeding potash continuously from storage tank 28 into Vthe vessel communicating therewith. If potassium sulfate is employed, the storage tank 28 communicates with the rst vessel of the series. Storage facilities for supplying continuously other soil enriching constituents, such as those hereinabove enumerated desirably communicate with the last Vessel of the series.

Blender 2l' receives dried product through a line 3i hereinafter described. This blender is provided with a suitable agitator 32 for agitating the mixture producing a substantially uniform blend which may be fed continuously through line 33 into a rotary kiln drier 34. This kiln drier 3A may be provided with a burner 130 and a line 35 through which dust formed in the drier and combustion gases flow into a dust separator 36. Solid materials separated in dust separator 35 are fed through a line 31 into discharge line 38 connecting the drier 34 with the cooler 39. Cooler 3S may be in the form of a rotary kiln equipped with a line 4l for supplying air or other cooling gas thereto. The cooling medium iiows countercurrent to the now of the hot dried granules and exits from the cooler 30 through a line 42 communicating with a dust collector :33. Solid material separating in dust collector 43 is discharged through a line M onto vibrating screens 45 where it mixes with dried product exiting from the cooler 39 through discharge line 45. Vibrating screens 45 eect separation of the ine granules from the coarse particles. The fine granules flow through lines lil into collecting channel :i8 from which they are transported to product collecting bin 49. The coarse particles iiow through lines into a collecting chamber 5I Vfrom which they are transported to a hammer mill 52 where they are nely ground. These iinely divided particles are conveyed through the line 3l into the blender 21. A line 53 desirably leads from the product bin 49 to the line 3i permitting the withdrawal of the desired amount of iinal product and the blending thereof with material fed to blender 2i to produce a mixture in the blender having the desired water content for eicient drying, as hereinabove disclosed.

The following examples are illustrative of the practice of the invention to produce complete fertilizers containing 12% N2, 12% P205 and 12% X20. It will be understood the invention is not limited to these examples. In these examples all parts are by weight:

Example I 16,600 pounds oi phosphate rock (34% P205), 2,740 pounds of triple superphosphate (48% P205) and mixed acid consisting of 36,990 parts ci 42% nitric acid and 6,150 parts of 94% sulfuric acid are introduced into the acidulator. The acidulated materialthus contains 35% water. It is agitated for ten minutes withoutexternal cooling. At the endv of the acidulation, the temperature of the mass is about '70 C. rEhe acidolated mass weighing 61,800 pounds is then introduced into the ammoniator. During acidulation 167 pounds of Sili, 233 pounds of NO2 and 280 pounds of water leave the acidulator in the form of gases which may be passed through the fume scrubber to recover the silicon uoride and nitrogen dioxide. 4,290 pounds of ammonia are employed to effect the ammoniation. IThis corresponds to .675 mol of ammonia per equivalent of acid used in the acidulation step.

900 pounds of water and 11,420 pounds of potassium chloride are introduced into the first and last of the three animoniation vessels, respectively, while agitating. The ammoniation is eiected at a temperature near the boiling point of the mixture and takes about two hours. 12,990 pounds of water are evaporated during the ammoniation.

The ammoniated slur-ry consisting of 65,420 pounds of which 15% is water, is introduced into the blender where it is mixed with 87,400 pounds of dried product having a particle size such that A it all passes an 8 mesh screen and 60% passes through a 50 mesh screen. rfhus, a total of 87,400 pounds of dry product are mixed with the ammoniated slurry producing a mixture containing 152,820 pounds having a water content of 7.5% and a liquid content of about.35% at C. lThis mixture is passed through the drier entering at 70 C. and leaving at 110 C. It then passes through the cooler where it is cooled to '70 C. 143,400 pounds of Vdry product are thus produced. In the drier and cooler approximately 9,420 pounds of water are removed along with approximately 200 pounds of nitrogen salts. The dried product is passed through vibratory screens producing approximately 56,000 pounds of nal product having a particleV size such that it all passes an 8 mesh screen, which isl passed to product storage, 18,570 pounds of nely divided product which is'recirculated to the blender and 68,830 pounds of coarse particles which are ground and then recirculated to the blender. The iinal dry product passed to product storage is in the form of hard, solid granules which are homogeneous, non-caking, free nowing and chemically stable. The product has a water content of about 1%.

9 Example II 36 pounds of phosphate rock (34% P205), 5.7 pounds of phosphoric acid (85% H3P04), 22 pounds of sulfuric acid (94.7% H2SO4) and 67.5 pounds of nitric acid (42% HNOS) are introduced into the acidulator. The acidulated material thus contains about 32% water. 1t is agitated for ten minutes without external cooling. At the end of the acidulation, the temperature of the mass is about 73 C. The acidulated mass weighing 129.7 pounds is then introduced into the ammoniator. During the acidulation, a total of about 1.5 pounds of gas, consisting of SiF4, N02, and water, leave the acdulator and may be passed through the fume scrubber to recover the silicon fluoride and nitrogen dioxide. 11.9 pounds of ammonia are employed to effect the ammoniation. This corresponds to .618 mol of ammonia per equivalent of acid used in the acidulation step.

24.6 pounds of potassium chloride (62.5% E20) are introduced into the lastl of three ammoniation Vessels while agitating. The ammoniation is eiected at a temperature near the boiling point of the mixture and takes about two hours. l2 pounds of water are evaporated during the ammoniation.

The ammoniated slurry consisting of 154.2 pounds, of which 18% is water, is introduced into the blender where it is mixed with 216.0 pounds of dried product having a particle size such that it all passes an 8 mesh screen and 60% passes through a 50 mesh screen. Thus, a total of 216.0 pounds of dried product are mixed with the ammoniated slurry producing a mixture containing 370.2 pounds having a water content of 7.5% and a liquid content of about 35% at 70 C. This mixture is passed through the drier entering at 70 C. and leaving at 110 C. It then passes through the cooler where it is cooled to 70 C. 344.0 pounds of dry product are thus produced. In the drier and cooler approximately 25.5 pounds of water are removed along with approximately 0.7 pound of nitrogen salts. The dried product is passed through vibratory screens producing approximately 128 pounds of nal product having a particle size such that it all passes an 8 mesh screen, which is passed to product storage, 46 pounds of finely divided product, which is recirculated to the blender, and 170 pounds of coarse particles which are ground and then recirculated to the blender. The final dry product passed to product storage is in the form of hard, solid granules which are homogeneous,

non-caking, free-flowing and chemically stable. r

The product has a water content of about 1%.

It will be noted this invention provides a process for producing complete fertilizers of lessened hygroscopicity in the form of hard, non-caking granules, substantially completely stabilized chemically and practically each particle of which is a complete fertilizer, the particles being nonsegregating, homogeneous and substantially alike in chemical composition. The complete fertilizer is made of relatively low cost raw materials, the P205 content being derived chiefly from phosphate rock, and the nitrogen content from nitric acid and ammonia. Furthermore, the process of this invention eects acidulation and ammoniation rapidly and eiciently; the reaction masses in the various steps of the process are in the form of slurries which are relatively freeowing, permitting the ready mechanical handling thereof without fouling the equipment.

In the specification all percentages are by weight, unless otherwise indicated.

Since diierent embodiments of the invention could be made without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

l. A process for preparing fertilizers which comprises the following steps: step 1, treating phosphate rock with a mixed acid containing nitric acid and at least one acid from the group consisting of sulfuric and phosphoric acids in the proportions of from about 7 to about 20 equivalents of mixed acid per mol of P205 in the phosphate rock, said mixed acid containing nitric acid in amount of from about 40% to about 80% of the acid equivalents, the acidulation of the rock being carried out in the presence of water amounting to from about 15% to about 40% by weight of the total mixture; step 2, ammoniating the acidulated material employing from about 0.6 to about 0.8 mol of ammonia per equivalent of acid and suflicient water so that the ammoniated material leaving the ammoniation treatment contains from about 15% to about 30% by weight of water and incorporating a potassium salt in amount to produce a nal product containing from about 7% to about 20% by Weight of H2O; step 3, mixing the material from step 2 with a portion of the dry product from step 4 to produce a mixture containing from about 15% to about 45% by weight of liquid at a temperature of from about 60 to about 80 C.; and step 4, drying the resultant mixture to produce a fertilizer containing not more than about 2% by weight of moisture and withdrawing as product dried mixture not passed to step 3.

2. The process defined in claim 1 in which the potassium salt is incorporated in the ammoniated material prior to completion of the ammoniation of said material.

3. A process for preparing fertilizers which comprises the following steps: step 1, treating phosphate rock with a mixed acid containing nitric acid and at least one acid from the group consisting of sulfuric and phosphoric acids in the proportions of from about 9 to about 16 equivalents of mixed acid per mol of P205 in the phosphate rock, said mixed acid containing nitric acid in amount of from about 60% to about of the acid equivalents, the acidulation of the rock being carried out in the presence of water amounting to from about 15% to about 40% by weight of the total mixture; step 2, ammoniating the acidulated material at a tempera ture near its boiling point employing from about 0.6 to about 0.8 mol of ammonia per equivalent of acid and sufficient water so that the ammoniated material leaving the ammoniation treatment contains from about 15% to about 18% by weight of water and incorporating a potassium salt in amount to produce a final product containing from about 7% to about 20% by weight of KzO; step 3, mixing the resultant material at a temperature of from about 75 to about C. with from about 25% to about 65% by weight of the product produced in step 4 at a temperature of from about 55 to about 65 C. to produce a mixture at a temperature oi from about 60 to about 80 C. containing from about 25% to about 35% by weight of liquid; and step 4, drying the resultant mixture to produce a fertilizer containing not more than about 2% by 11 weight of moisture and withdrawing as product dried mixture notpassed to step 3.

4. A continuous process for preparing fertilizers which comprises the following steps: step 1, continuously introducing phosphate rock and mixed acid containing nitric acid and at least one acid from-the group consisting of sulfuric and phosphoric acids in the proportions of from about to about 20 equivalents of mixed acid per mol of P205 in the phosphate rock, said mixed fl acid containing nitric acid in amount of from about 40% to about 80% of the acid equivalents, the acidulation of the rock being carried out in the presence of Water amounting to from about to about40% by weight of the total mixture; step 2, continuously discharging the acidulated rock from the acidulation zone and introducing the same into an ammoniation zone into which ammonia' is continuously introduced in amount of from about 0.6 to about 0.6 mol oi ammonia per equivalent of acid and from which ammoniated material is continuously Withdrawn, suflicient water being introduced into the ammoniation zone so that the ammoniated material continuously leaving the ammoniation zone contains from about 15% to about 30% by weight of Water, and continuously incorporating a potassium salt in amount to produce a nal product containing from about 7% to about 20% by weight of K2O; step 3, continuously mixing the potassium salt-containing mixture with a portion of dry fertilizer produced in step 4 to form a mixture containing from about 15% to about 45% by weight of liquid at a temperature of from about 60 to about 80 C.; and step 4, continuously passing this mixture through a drier to produce a fertilizer containing not more than about 2% by weight of moisture and withdrawing as product dried mixture not passed to step 3.

5. A continuous process for preparing fertilizers which comprises the foliowing steps: step l, continuously introducing phosphate rock and mixed acid containing nitric acid and at least one acid from the group consisting of sulfuric and phosphoric acids in the proportions of from about 9 to about 16 equivalents of mixed acid per mol of P205 in the phosphate rock, said mixed acid containing nitric acid in amount of from about 60% to about 80% of the acid equivalents, the acidulation of the rock being carried out in the presence of water amounting to from about 15% to about 40% by weight of the total mixture; step 2, continuously discharging the acidulated rock from the acidulation zone and introducing the same into an ammoniation zone into which ammonia is continuously introduced in amount of from about 0.6 to about 0.8 mol of ammoniaper equivalent of acid and from which ammoniated material is continuously withdrawn, sufficient water being introduced into the ammoniation zone so that the ammoniated material continuously leaving the ammoniation treatment contains from about 15% to about 18% by weight of water, and continuously incorporating potassium salt in amount to produce a iinal product containing from about 7% to about 20% by weight of K2O; step 8, continuously mixing the potassium salt-containing mixture with a portion of dry fertilizer produced in step 4 to form a mixture containing from about to about 35% by weight of liquid at a temperature of from about 60 to about 80 C. and step 4, continuously passing this mixture through a drier to produce a vfertilizer containing not more than about 2% by weight of moisture and 12 withdrawing as product dried mixture not passed to step 3.

6. A process for preparing fertilizers which comprises the following steps: step 1, treating phosphate rock with a mixed acid consisting of nitric and sulfuric acids in the proportions of from about 7 to about 20 equivalents of mixed acid per mol of P205 in the phosphate rock, said mixed acid containing nitric acid in amount of from about 40% to about 80% of the acid equivalents, the acidulation of the rock being carried out in the presence of water amounting to from about 15% to about 40% by weight of the total mixture; step 2, ammoniating the acidulated material employing from about 0.6 to about 0.8 mol of ammonia per equivalent of acid and sufficient water so that the ammoniated material leaves the ammoniation treatment containing from about 15% to about 30% by weight of Water, and incorporating a potassium salt in amount to produce a nal product containing from about '7% to about 20% by weight of KZO; step 3, mixing the material from step 2 with a portion of the dried product from step 4 to produce a mixture containing from about 15% to about 45% by weight of liquid at a temperature of from about 60 to about 80 C.; and step 4, drying the mixture from step 8 to produce a product containing not more than about 2% by weight of moisture, and .withdrawing as product dried mixture not passed to step 3.

7. The process as defined in claim 6, in which up to 30% of triple superphosphate based on the weight of the phosphate rock is added to the phosphate rock subjected to aciduiation.

8. A process for preparing fertilizers which comprises the following steps: step i, treating phosphate rock with a mixed acid consisting of nitric and sulfuric acids in the proportions of from about 9 to about 16 equivalents of mixed acid per mol of P205 in the phosphate rock, said mixed acid containing nitric acid in amountof from about 60% to about 80% of the acid equivaient, the acidulation of the rock being carried out in the presence of water amounting to from about 15% to about 40% by weight oi the total mixture; step 2, ammoniating the acidulatcd material employing from about 0.6 to about 0.8 mcl of ammonia per equivalent of acid and sumcient water so that the ammoniated material leaves the ammoniation treatment containing from about 15% to about 30% by weight oi water, the ammoniation during the initial stages at least being carried out at a temperature near the boiling point of the material subjected to ammoniation, and incorporating potassium chloride during the ammoniation treatment in amount to produce a product containing from about 7% to about 20% by weight of B120; step 3, mixing the resultant material from step 2 with crushed particles produced in step 6 to form a mixture containing from about 25% to about 35% by weight of liquid at a temperature of from about 60 to about 80 C.; step 4, drying the mixture from step 3 to produce a product containing not more than about 2% by weight oi' moisture; step 5, cooling the dried product; and step 6, screening the dried product to separate the coarse particles from the nner particles, crushing the coarse particles, recirculating the crushed particles to step 3 for mixing with the material produced in step 2 and withdrawing as product finer particles produced in the screening of the dried product.

9. Theprocess as defined in claim 8, in which 13 from about 15% to about 20% of triple superphosphate based on the weight of the phosphate rock is mixed with the phosphate rock subjected to acidulation.

10. A process for preparing a complete fertilizer which comprises the following steps: step 1, treating phosphate rock with a mixed acid consisting of nitric and phosphoric acids in the proportions of from about 9 to about 16 equivalents of mixed acid per mol of P205 in the phosphate rock, said mixed acid containing nitric acid in amount of from about 70% to about 80% of the acid equivalents, the acidulation of the rock being carried out in the presence of water amounting to from about 15% to about 40% by weight of the total mixture; step 2, ammoniating the acidulated material employing from about 0.6 to about 0.8 mol of ammonia per equivalent of acid and sucient Water so that the ammoniated material leaves the ammoniation treatment containing from about 15% to about 30% by Weight of water and incorporating a potassium salt in the ammoniated material in amount to produce a iinal product containing from about 7% to about l20% by weight of KzO; step 3, mixing the resultant material from step 2 with a portion of the dried product from step 4 to produce a mixture containing from about 15% to about 45% by Weight of liquid at a temperature of from about 60 to about 80 C.; and step 4, drying the mixture from step 3 to produce a product containing not more than about 2% by weight of moisture and withdrawing as product dried mixture not passed to step 3.

11. A process for preparing a complete fertilizer which comprises the following steps: step 1, treating phosphate rock with a mixed acid consisting of nitric and phosphoric acids in the proportions of from about 9 to about 16 equivalents of mixed acid per mol of P205 in the phosphate rock, said mixed acid containing nitric acid in amount of from about 70% to about 80% of the acid equivalents, the acidulation of the rock being carried out in the presence of water amounting to from about 15% to about 40% by weight of the total mixture; step 2, ammoniating the acidulated material employing from about 0.6 to about 0.8 mol of ammonia per equivalent of acid and suiiicient water so that the ammoniated material leaves the ammoniation treatment containing from about 15% to about 18% by weight of water, the ammoniation during the initial stages at least being carried out at a temperature near the boiling point of the material subjected to ammoniation, and incorporating a potassium salt in the ammoniated material in amount to produce a product containing from about 7 to about 20% by weight of K2O; step 3, mixing the resultant material from step 2 with a portion of the dried product from step 4 to produce a mixture containing from about 25% to about 35% by weight of liquid at a temperature of from about 60 to about 80 C.; and step 4, drying the mixture from step 3 to produce a product containing not more than about 2% by weight ofy moisture and withdrawing as product dried mixture not passed to step 3.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,788,828 Goldberg Jan. 13, 1931 1,849,989 Moore Mar. 15, 1932 1,916,429 Larsson July 4, 1933 1,948,520 Harvey Feb. 27, 1934 2,102,831 Brill Dec. 21, 1937 2,448,126 Shoeld Aug. 31, 1948 FOREIGN PATENTS Number Country Date 357,473 Great Britain Sept. 24, 1931 

1. A PROCESS FOR PREPARING FERTILLIZERS WHICH COMPRISES THE FOLLOWING STEPS; STEP 1, TREATING PHOSPHATE ROCK WITH A MIXED ACID CONTAINING NITRIC ACID AND AT LEAST ONE ACID FROM THE GROUP CONSISTING OF SULFURIC AND PHOSPHORIC ACIDS IN THE PROPORTIONS OF FROM ABOUT 7 TO ABOUT 20 EQUIVALENTS OF MIXED ACID PER MOL OF P2O5 IN THE PHOSPHATE ROCK, SAID MIXED ACID CONTAINING NITRIC ACID IN AMOUNT OF FROM ABOUT 40% TO ABOUT 80% OF THE ACID EQUIVALENTS, THE ACIDULATION OF THE ROCK BEING CARRIED OUT IN THE PRESENCE OF WATER AMOUNTING TO FROM ABOUT 15% TO ABOUT 40% BY WEIGHT OF THE TOTAL MIXTURE; STEP 2, AMMONIATING THE ACIDULATED MATERIAL EMPLOYING FROM ABOUT 0.6 TO ABOUT 0.8 MOL OF AMMONIA PER EQUIVALENT OF ACID AND SUFFICIENT WATER SO THAT THE AMMORIATED MATERIAL LEAVING THE AMMONIATION TREATMENT CONTAINS FROM ABOUT 15% TO ABOUT 30% BY WEIGHT OF WATER AND INCORPORATING A POTASSIUM SALT IN AMOUNT TO PRODUCE A FINAL PRODUCT CONTAINING FROM ABOUT 7% TO ABOUT 20% BY WEIGHT OF K2O; STEP 3, MIXING THE MATERIAL FROM STEP 2 WITH A PORTION OF THE DRY PRODUCT FROM STEP 4 TO PRODUCE A MIXTURE CONTAINING FROM ABOUT 15% TO ABOUT 45% BY WEIGHT OF LIQUID AT A TEMPERATURE OF FROM ABOUT 60* TO ABOUT 80* C.; AND STEP 4, DRYING THE RESULTANT MIXTURE TO PRODUCE A FERTILIZER CONTAINING NOT MORE THAN ABOUT 2% BY WEIGHT OF MOISTURE AND WITHDRAWING AS PRODUCT DRIED MIXTURE NOT PASSED TO STEP
 3. 